Particles of a resin such as polyphenylene ether are obtained through a polymerization step of emulsion polymerization, suspension polymerization, solution polymerization, or the like, followed by a particle precipitation step, dry grinding of a resin material, and so forth. Accordingly, resin particles are generally produced with an undefined or spherical shape.
Conventionally, resin particles of various different forms have been developed for a variety of objectives such as an objective of improving mechanical properties and handleability of resin particles, an objective of suppressing particle fragmentation due to particle collisions during mixing, stirring, or air conveyance, an objective of improving cleaning properties, an objective of improving powder handleability in a hopper during melt-kneading, and an objective of improving slip properties of cosmetics.
For example, one problem that may be experienced in handling of powder in a hopper for melt-kneading or the like is that feeding of the powder using a powder feeding device formed by a weighing feeder may cause flushing of the powder (i.e., a phenomenon may occur in which the powder forms a liquid-like state and passes straight through a screw part of the powder feeding device). This flushing results in poorer feeding accuracy, and may also cause the fed material to pass through the screw at once. In continuous operation of a weighing feeder, operation is often performed at reduced powder feeding device capability to prevent flushing. However, this also reduces productivity.
Furthermore, when a powder having a high fine content is used, this may cause problems such as reduced yield due to fine powder scattering, malfunction due to encroachment into an extruder or the like, and filter blocking from a drying step to an air conveyance step.
The following describes examples of developments that have been made in relation to resin particles of specific shapes such as mentioned above. PTL 1 reports highly spherical particles of polyphenylene ether. Moreover, a technique for producing spherical polyphenylene ether has been proposed that involves adding an aqueous solution of a water-soluble organic polymer to an organic solvent solution containing dissolved polyphenylene ether, and then performing deliquoring treatment while maintaining the polyphenylene ether in a dispersed state (PTL 2). Furthermore, particles having cracks have been proposed, and it has also been proposed that a shape capable of trapping fine powder exhibits an inhibitive effect with respect to bridging (PTL 3).
PTL 4 to 9 disclose compression granulation of polyphenylene ether powder to increase the loose apparent specific gravity of the polyphenylene ether powder with the aim of improving handleability. These techniques focus on adjusting particle size, reducing fine content, and improving efficiency of powder transport, storage, and feeding to an extruder through compression and grinding of polyphenylene ether powder.